The invention relates to a feed pump for fluidic media.
Described in EP 0 061 630 A1 is a gear pump for metered feeding of lacquers, which pump is provided with a pump inlet and a pump outlet as well as with two gears that mesh with each other, which gears are rotatably supported inside a pump housing by a powered drive shaft and a stationary support shaft. This known arrangement is provided with a flushing-channel system for flushing of gaps between the gears, the shafts, and the pump housing prior to a color exchange, the flushing-channel system displaying at least one flush chamber and one closable inlet for a flushing agent and several flushing channels connected to the flushing chamber.
In this connection, known from EP 1 164 293 A2 is the arrangement of the flushing channels in the region of the drive shaft such that the flushing agent flows through the bearing gap of the drive shaft over the entire bearing width of the respective bearing sites, from the outside inwardly towards the front of the gear.
Using this known arrangement, the color residue is again and again inadequately rinsed out, so that during operation the situation arises where, to a greater or lesser degree, mixtures of colors are present.
Known from GB 322 778 is a feed pump that is designed as a gear pump in which the lubrication of the sleeve bearings takes place through the actual fed medium itself.
The sucking in of the fed medium, which serves as the lubricant, is caused by the differential pressure prevailing between the suction side and the pressure side in the product channel, and after the lubrication of the sleeve bearings the lubricant is released into the product channel at the suction side of the pump. Thus, the lubricant is, on the one hand, pushed by the pump pressure into the space of the sleeve bearings and, on the other hand, sucked out of the sleeve bearings by the low pressure prevailing at the suction side.
If a product exchange takes place in the product channel, then a dismantling of the feed pump is necessary in order to cleanse the sleeve bearings of the previously-fed product so that the mixing of products is prevented. This operation is complex and time-consuming.
The invention is based on the task of creating an arrangement whereby dismantling of the pump and the cleansing of the sleeve bearings will no longer be necessary, but rather the cleansing is to take place though the fed medium itself and it is to be possible to monitor from the outside whether this cleansing has completely occurred.
Express differently, in a feed pump having the form of a rotary piston pump or a gear pump and being arranged in a product channel, it is proposed that a guide channel be additionally provided, which guide channel is arranged on the suction side of the pump for both sleeve bearings and which is connected to the connecting channels that are designed to feed the fed medium lubricating the sleeve bearings and lead to the suction side of the pump. Arranged in these connecting channels are valve plungers having a constriction, which plungers can be shifted from one position, in which they do not hinder the fed medium (which lubricates the sleeve bearings) towards the suction side of the product channel, into another position in which this channel serving the recirculation of the lubricant is closed. Here, not only is the connecting channel closed, but also the valve plunger has a length in this region that corresponds to the length of the connecting channel, in order to avoid dead zones. Further, the valve plunger displays a constriction that, when the connecting channel has been closed by the shifting of the plunger, makes possible a passage from the channel that connects to the sleeve bearings to a control channel, so that henceforth fed medium is guided by the pump through the sleeve bearings to the control channel. By this means, it can be easily determined at the emission end of the control channel whether the sleeve bearings have been completely cleansed during a material exchange or whether a mixture of products is still dispensed. As soon as the sleeve bearings have been completely cleansed, the valve plungers are shifted back into their original position and henceforth the lubrication of the sleeve bearings takes place in the previously conventional manner, i.e. the fed medium is again recirculated to the suction side of the product channel.
The above-described arrangement can also be used to undertake product testings at the end of the product channel, for example to enable the removal of test samples that are then investigated and to enable the quality of the product fed through the pump to be controlled.
According to a further feature of the invention, the constriction possesses a length that corresponds to the distance of the mouth of the control channel in the housing cover from the mouth of the connecting channel at the outside of the pump housing.